1. Field of the Invention
The present invention is in the field of fluid dispensing apparatus and methods. More particularly, the present invention relates to fluid dispensing apparatus and methods for analytical systems used in a variety of environments to carry out analytical, laboratory, and clinical procedures. These analytical systems are generally automatic or semiautomatic and are used in hospital and clinical environments. Generally such analytical systems are used to process patient specimens including, for example, tissue and bodily fluid samples, for detecting the presence of various chemical compounds and organisms therein.
2. Discussion of the Related Technology
Conventional chemical analyzers and incubators have been known which employ fluid dispensing apparatus. For example, microbiological analytical systems are known currently which carry out automated antimicrobic susceptibility testing procedures using both photometric and fluorometric detection methods. U.S. Pat. Nos. 4,643,879; 4,676,951; and 4,681,741, describe certain features of such a system.
Generally, the conventional analyzer includes a vertically extending annular incubation chamber within which is loaded a plurality of specimen trays each defining plural recesses within which a portion of selected specimen material is placed for processing. On the specimen trays the recesses are arranged in rows and columns to form a rectangular grid. The specimen trays in a horizontal disposition and each with an individual cover are stacked vertically one above the other and are vertically spaced apart in plural tray racks within the incubation chamber.
The incubation chamber includes a carousel moving the specimen trays in their racks around the annulus of the incubation chamber. A column structure extends vertically up the center of the incubation chamber annulus, and a carrier is vertically movable on this column. The tray racks are moved about the incubation chamber to bring a selected rack in front of the carrier. This carrier includes an extensible shelf which may be extended into the tray storage rack to lift a particular specimen tray therefrom. The rack itself is configured so that the tray cover stays in the rack. Consequently, the carrier shelf receives the tray without its cover so that the recesses within which the specimens are carried are open while the tray is on the carrier shelf. The specimen trays are formed of translucent or transparent material, and the carrier shelf is open below each recess.
On the carrier a first work station includes an elongate bar-like photometric analyzer aligning with the rows of specimen recesses. In order to photometrically analyze the contents of the recesses in a particular row of the recesses the shelf is extended or retracted to align the particular specimen recess row with the photometric analyzer. The photometric sensor has a plurality of separate sensor heads each of which aligns with one of the recesses in the particular row, and light transmission through the specimen material is used to detect certain changes, such as turbidity.
The carrier also includes a shuttle member moving from side to side over the specimen tray and carrying a fluorometric analyzer. The fluorometric analyzer has a single sensor head and is brought into alignment with a particular specimen recess by extension or retraction of the shelf, in conjunction with side to side movement of the shuttle. Similarly, the shuttle carries a fluid dispensing head from which various liquid reagents may be dispensed into particular ones of the specimen recesses. This fluid dispensing head includes a separate fluid dispensing nozzle for each of the reagents. These nozzles are arranged in a rectangular grid so that the coordinates of each nozzle opening relative to the shuttle member are known. By extension and retraction of the tray and side to side movement of the shuttle member, a particular nozzle opening of the fluid dispensing head may be brought into vertical congruence with a particular recess of the specimen tray for dispensing of reagent liquid into the recess.
However, experience has shown that having the fluid dispensing head permanently carried on the shuttle member results in some disadvantages. First of all, the movements of the carrier and shuttle in the incubation chamber require that the liquid reagent sources be connected to the fluid dispensing head with conduits of considerable length. The length of these conduits becomes a disadvantage when one considers the small volume of the reagents which must be dispensed into the specimen recess, along with the precision with which these reagents must be measured out.
Additionally, some of the reagents themselves are acidic, caustic or otherwise corrosive. Consequently, taking the reagent dispensing head into the incubation volume exposes many parts of the incubator to the possibility of deterioration from the corrosive natures of the reagent liquids. Also, the incubator itself involves an environment of elevated temperature which may result in evaporation of volatile constituents of some of the reagents.
Still additionally, the reagents which do experience evaporation of some constituent thereof may undergo an increase in their viscosity so that they do not dispense accurately. In extreme cases, the reagent may evaporate to the point of leaving a crust of solids which blocks the individual dispensing nozzle for that reagent. Even in those cases where the reagent crust does not block the dispensing nozzle, the presence of the crust can result in dispensed reagent going astray instead of into the intended specimen recess. All of these difficulties represent possible operating interruptions for a clinical analyzer, with attendant possible loss of test results for the specimens in process, and delay of processing of other specimens awaiting analysis. In every case, evaporation and crusting of reagent represents loss of reagent which is not used in processing specimens.